//! Tracing subscriber initialisation.
//!
//! Terminal (TTY): human-readable format with colors
//! Pipeline (non-TTY): JSON output for VictoriaLogs
//! Override via `APP_LOG_FORMAT=json|pretty` env var.

use crate::msg_json_fmt::MsgJsonFormat;

use once_cell::sync::Lazy;
use std::io::IsTerminal;
use std::str::FromStr;
use tracing_subscriber::Layer;
use tracing_subscriber::{
    fmt::{self, format::FmtSpan},
    layer::SubscriberExt,
    util::SubscriberInitExt,
    EnvFilter,
};

/// Global instance identifier, resolved once at startup.
/// Priority: `INSTANCE_ID` env var → system hostname → `"unknown"`.
pub static INSTANCE_ID: Lazy<String> = Lazy::new(|| {
    std::env::var("INSTANCE_ID")
        .ok()
        .filter(|s| !s.is_empty())
        .or_else(|| {
            hostname::get()
                .ok()
                .and_then(|h| h.into_string().ok())
                .filter(|s| !s.is_empty())
        })
        .unwrap_or_else(|| "unknown".to_string())
});

/// Returns the platform-wide instance identifier for this process.
pub fn instance_id() -> String {
    INSTANCE_ID.clone()
}

/// Determines the log format based on environment and TTY detection.
fn use_json() -> bool {
    match std::env::var("APP_LOG_FORMAT").as_deref() {
        Ok("json") => true,
        Ok("pretty") => false,
        _ => !std::io::stdout().is_terminal(), // TTY → pretty, non-TTY → json
    }
}

/// Initialises the global tracing subscriber.
///
/// TTY terminals get human-readable output with colors.
/// Non-TTY (pipes, container logs) get JSON for log aggregation.
/// `APP_LOG_FORMAT=json|pretty` overrides auto-detection.
/// `RUST_LOG` env var controls the log level filter.
///
/// Pass `defer = true` when OTLP will be initialized afterwards via `init_otlp()`.
pub fn init_tracing_subscriber(level: &str, defer: bool) {
    let env_filter = EnvFilter::try_from_default_env()
        .or_else(|_| EnvFilter::from_str(level))
        .unwrap_or_else(|_| EnvFilter::from_str("info").expect("default log level"));

    let fmt_layer: Box<dyn Layer<_> + Send + Sync> = if use_json() {
        let mut layer = fmt::layer().event_format(MsgJsonFormat);
        layer.set_span_events(FmtSpan::CLOSE);
        <_ as Layer<_>>::boxed(layer)
    } else {
        let mut layer = fmt::layer()
            .with_target(false)
            .with_level(true)
            .with_ansi(std::io::stdout().is_terminal())
            .pretty();
        layer.set_span_events(FmtSpan::CLOSE);
        <_ as Layer<_>>::boxed(layer)
    };

    let registry = tracing_subscriber::registry()
        .with(env_filter)
        .with(fmt_layer);

    if defer {
        return;
    }

    let _ = registry.try_init();
}